Expression of PPARγ and PTEN in human colorectal cancer: An immunohistochemical study using tissue microarray methodology.

Abstract

Although aberrations of peroxisome proliferator-activated receptor γ (PPARγ) and phosphatase and tensin homolog (PTEN) expression have been identified in several other cancer types, certain previous studies have revealed that PPARγ is abundant in normal and malignant tissue in the colon. The question of whether aberrant PTEN is involved in the initial stage or is a later event during colorectal carcinogenesis remains controversial. Relatively few studies have focused on the correlation of expression of PPARγ and PTEN in various tissues. In the present study, paraffin-embedded blocks from 139 patients with CRC, 18 adenomatous polyps and 50 paired paracancerous benign mucosas were selected and analysed in 4 tissue microarray (TMA) blocks comprising 104, 72, 130 and 54 cores, respectively. Expression of PPARγ and PTEN was examined using immunohistochemical staining on TMAs. There were no significant differences in the expression of PPARγ (P=0.055) and PTEN (P=0.100) between the colorectal cancers, adenomas and paracancerous mucosas. However, correlations of PPARγ expression with clinical stage (P=0.004) and PTEN expression with histological grade (P=0.006) and distant metastasis (P=0.015) were demonstrated in the CRC specimens. Although the differences in PPARγ and PTEN protein expression in human colorectal cancer may not be considered as early diagnostic markers, our results indicate that CRCs with a low expression or deletion of PTEN may progress towards invasion and even metastasis; thus, PTEN may have potential as a prognostic marker in human CRC.

Immunophenotype of the investigated antigens (PPARγ and PTEN) in three colorectal tissues (original magnification, ×100). Positive stainings of PPARγ were located in the cell nuclei, while those of PTEN were in the cytoplasm. (A) HE staining of the TMA section of colorectal cancer tissue. (B, C and D) PPARγ expression in benign mucosa, adenomas and cancer tissues. (E, F and G) PTEN expression in benign mucosa, adenomas and cancer tissues, respectively.